If you are looking for more stability and higher clocks then 2T is the setting needed. 1T is command per clock. Setting 2T can make all the difference when pushing for high clocks. It will effect every machine in a different way but generally for more stability and highest clocks achievable- 2T. You will need to find the balance of high clocks 2T or lower clocks 1T. All timings in-between also need to be adjusted and tested accordingly. This is a very long task and is not to be rushed. Use Memtest 86 for testing.

Get a pen and paper handy as you will need to record what settings work and what don't. Test for speed versus performance and timings used.